Exp) Option b is the correct answer.

Biological filters are devices to culture microorganisms that will perform a given task for us. Different types of organisms will perform different tasks. Part of the art of designing and using biofilters is to create an environment that will promote the growth of the organisms that are needed.

Statement 1 is correct: A biofilter system helps in waste treatment by removing uneaten fish feed. They make use microorganisms which are capable of degrading a number of compounds like uneaten fish feed and thus helps in breaking down pollutants.

Statement 2 is correct: Ammonia is removed from an aquarium system through the use of a biofilter. The biofilter provides a substrate on which nitrifying bacteria grow. These nitrifying bacteria consume ammonia and produce nitrite, which is also toxic to fish. Other nitrifying bacteria in the biofilter consume nitrite and produce nitrate.

Statement 3 is incorrect: Biofilters are used to reduce (not increase) the amount of phosphorus in water. Submerged flow biofilters, utilising a filter media were used to remove nitrogen and phosphorus from a synthetic fish farm water. The cyclic aerated/unaerated combined nutrients removal system

achieved approximately 40 percent phosphorus removal, complete nitrification and 40 percent denitrification.

Source:https://www.researchgate.net/publication/351090677_TREATMENT_OF_WATER_USING_BIOFILTER_IN_RECIRCULATING_AQUACULTURE https://www.fdacs.gov/Consumer-Resources/Recreation-and-Leisure/Aquarium-Fish/Aquarium-Water-Quality-Nitrogen-Cycle https://cals.arizona.edu/azaqua/ista/ISTA7/RecircWorkshop/Workshop%20PP%20%20%26%20Misc%20Papers%20Adobe%202006/5%20Solids%20Capture/Solids%20Control.pdf